Conventionally, a switch-mode power supply for power factor correction rectifies an alternating input voltage using a bridge diode, and smoothes the rectified output voltage using a capacitor for a booster-type switch-mode power supply. The rectified output from the bridge diode is controlled by a choke coil for the booster-type switch-mode power supply, a switching semiconductor switch for the booster-type switch-mode power supply, a rectifier diode for the booster-type switch-mode power supply, and a power factor correction control circuit, such that a capacitor charge voltage as an output of the smoothing electrolytic capacitor when an inputted current is sinusoidal and a boosting operation is performed becomes an output voltage set by a resistance for setting an output voltage. Accordingly, as a feedback control is typically performed in a booster-type switch-mode power supply so as not to respond to a commercial frequency, an output response to a sudden change of an input and a sudden change of a load may easily delay, and thus overshoot of an output voltage may easily produced.
Thus, as illustrated in FIG. 9, a conventional technique described in Patent Literature 1 proposes a direct-current source circuit provided with: a rectifying means (D10 in FIG. 9) for rectifying and smoothing a commercial alternating-current source; a boosting inductance element (L10 in FIG. 9); a switching means (Q10 in FIG. 9) for connecting and disconnecting a current through the inductance; a direct voltage generating means (C20 in FIG. 9) for rectifying and smoothing an output from the switching means to obtain a direct output voltage; a switch control means (an output voltage control circuit, an oscillation control unit, and a driver in FIG. 9) for variably controlling a switching frequency of the switching means based on an excitation voltage of the inductance element and the output, and at least stabilizing an output from the direct-current source circuit; and a switching operation stopping means (an overvoltage detecting unit and an overcurrent detecting unit in FIG. 9) configured to detect a voltage level corresponding to the commercial alternating-current source and to stop a switching operation of the switching means when the voltage level is higher than a predetermined threshold value. According to this direct-current source circuit, when the voltage level of the commercial alternating-current source is equal to or higher than the predetermined, the switching operation of the switching means in an active filter is stopped. With this, under a condition such that the commercial alternating-current source is a high voltage and with a light load, for example, it is possible to avoid an excessive increase of the voltage in the inductance element.
However, according to the conventional technique described in Patent Literature 1, as illustrated in FIG. 10 (FIG. 11 is a timing chart showing a timing chart in FIG. 9 in a wider timeline), in activation when the commercial alternating-current source is applied to the input of the direct-current source circuit, it is probable that an output voltage steeply increases and an intermittent oscillating operation of repeatedly oscillating and stopping oscillating may occur. If a cycle of repeating oscillating and stopping oscillating is within an audible region, a ringing sound may be possibly produced from the boosting inductance element and the like. Such a phenomenon is particularly noticeable when an input voltage is higher than an output voltage.
In contrast, a conventional technique described in Patent Literature 2 proposes a boost-chopper-type power factor correction power-supply device capable of setting a level of the output direct voltage to be a predetermined value, and correcting a power factor, and provided with: a rectifier for rectifying an inputted alternating voltage to obtain an pulsating voltage; a first switch element for applying the pulsating voltage to an inductor to supply a current for storing a magnetic energy; a second switch element for supplying a current corresponding to the magnetic energy; a smoothing capacitor for smoothing the current from the second switch element to obtain an output direct voltage; and a switch element controller for controlling switching between disconnection and conduction of the first switch element. According to the boost-chopper-type power factor correction power-supply device, an overvoltage detection signal is generated when the level of the pulsating voltage is higher than a predetermined threshold value, and the level of the output direct voltage is changed to be higher than the predetermined value based on the overvoltage detection signal.
Therefore, according to the boost-chopper-type power factor correction power-supply device, the rectifier rectifies the inputted alternating voltage and obtains the pulsating voltage, the first switch element applies the pulsating voltage to the inductor and supplies the current for storing the magnetic energy, and the second switch element supplies the current corresponding to the magnetic energy. The smoothing capacitor smoothes of the current from the second switch and obtains the output direct voltage, and the switch element controller controls between disconnection and conduction of the first switch element. Then, the output direct voltage is set to be the predetermined value, and the power factor is corrected. Further, the overvoltage detection signal is generated when a peak value of the pulsating voltage is higher than the predetermined threshold value, and the value of the output direct voltage is changed to a level higher than the predetermined value based on the overvoltage detection signal. With this, a current is prevented from being intermittently supplied to the inductor. Therefore, according to the boost-chopper-type power factor correction power-supply device disclosed in Patent Literature 2, generation of ringing sound in the boosting inductance element and the like in the direct-current source circuit of Patent Literature 1 is prevented.